Expansive reed populations-alien invasion or disturbed wetlands?

Kim Canavan,Martin P Hill,Iain D Paterson,Carla Lambertini

doi:10.1093/aobpla/ply014

Abstract

The tall-statured grasses in the genus Phragmites are dominant vegetation in wetlands worldwide and thus play a vital role in ecosystem functioning. As a result, Phragmites spp. are some of the most widely studied plants; particularly in areas where changes to their abundances have occurred, most notably in Europe and North America. In southern Africa a pattern of reed expansion has occurred in recent decades that has shown a similar trend to cryptic invasions reported in North America. This study used molecular techniques to explore the phylogeography of P. australis and P. mauritianus in the region to investigate whether the expansion is due to an alien invasion or local factors such as wetland disturbance. Three haplotypes were found and all haplotypes are presently considered African haplotypes (haplotype K for P. australis and haplotype V and AP for P. mauritianus). Both Phragmites spp. were found to have high genetic diversity. Microsatellite and grass-waxy analysis also found evidence of hybridization between the two species. No evidence was found for a recent cryptic invasion of non-native haplotypes in southern Africa. The expansion of P. australis and P. mauritianus is therefore most likely a result of anthropogenic activity. Identifying and mitigating the human-mediated factors that may be contributing to reed growth, such as eutrophication and sedimentation, should be the focus of future management protocols.

Highlights

Wetlands are considered one of the most valuable ecosystems as they are areas of naturally high species diversity, a diverse array of biological and physical processes, provide critical habitat structure and improve water quality (Cronk and Fennessy 2016)
Haplotype V was previously found in the P. mauritianus population in South Africa and in one sample from Equatorial Guinea labelled as P. vallatoria
The number of alleles amplified in each sample varied for P. australis and P. mauritianus; P. australis samples had an average of 2.16 ± 0.94 alleles amplified compared to only 1.56 ± 0.71 amplified for P. mauritianus

Summary

Introduction

Wetlands are considered one of the most valuable ecosystems as they are areas of naturally high species diversity, a diverse array of biological and physical processes, provide critical habitat structure and improve water quality (Cronk and Fennessy 2016) It is the dominant plants within these ecosystems that are most influential and as such, the greatest functional changes occur if the abundances of these species change (Richardson et al 2007). The expansion of certain reed populations in other regions has been attributed to cryptic invasion including parts of Canada (Lelong et al 2007) and South America (Guo et al 2013) Such phylogeographic work is under-represented in Africa (Lambertini et al 2012b)

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